From a3929d37616bafcab4d24756bd16217058059f9a Mon Sep 17 00:00:00 2001
From: Stefan Majer <stefan.majer@f-i-ts.de>
Date: Thu, 14 Apr 2022 07:31:52 +0200
Subject: [PATCH] only reboot every 3 days and spread in one day (#75)

---
 cmd/root.go          |  2 +-
 pkg/kernel/kernel.go | 19 +++++++++++++++----
 2 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/cmd/root.go b/cmd/root.go
index b1aab763..235cd3ef 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -66,7 +66,7 @@ func Run(spec *Specification, hal hal.InBand) (*event.EventEmitter, error) {
 	}
 
 	// Reboot after 24Hours if no allocation was requested.
-	go kernel.AutoReboot(24*time.Hour, func() {
+	go kernel.AutoReboot(3*24*time.Hour, 24*time.Hour, func() {
 		eventEmitter.Emit(event.ProvisioningEventPlannedReboot, "autoreboot after 24h")
 	})
 
diff --git a/pkg/kernel/kernel.go b/pkg/kernel/kernel.go
index 9a836c0b..dff4fa66 100644
--- a/pkg/kernel/kernel.go
+++ b/pkg/kernel/kernel.go
@@ -1,7 +1,9 @@
 package kernel
 
 import (
+	"crypto/rand"
 	"fmt"
+	"math/big"
 	"os"
 	"strings"
 	"time"
@@ -134,15 +136,24 @@ func Watchdog() {
 	}
 }
 
-// AutoReboot will start a timer and reboot after given duration
-func AutoReboot(after time.Duration, callback func()) {
-	log.Info("autoreboot", "after", after)
+// AutoReboot will start a timer and reboot after given duration a random variation spread is added
+func AutoReboot(after, spread time.Duration, callback func()) {
+	log.Info("autoreboot set to", "after", after, "spread", spread)
+	spreadMinutes, err := rand.Int(rand.Reader, big.NewInt(int64(spread.Minutes())))
+	if err != nil {
+		log.Warn("autoreboot", "unable to calculate spread, disable spread", err)
+		spread = time.Duration(0)
+	}
+	spread = time.Minute * time.Duration(spreadMinutes.Int64())
+	after = after + spread
+
+	log.Info("autoreboot with spread", "after", after)
 	rebootTimer := time.NewTimer(after)
 	<-rebootTimer.C
 	log.Info("autoreboot", "timeout reached", "rebooting in 10sec")
 	callback()
 	time.Sleep(10 * time.Second)
-	err := Reboot()
+	err = Reboot()
 	if err != nil {
 		log.Error("autoreboot", "unable to reboot, error", err)
 	}